The present invention relates to a yarn false twist texturing process and apparatus, and which has provision for controlling the twist imparted to an advancing yarn, and so as to permit the production of yarn of high quality.
U.S. Pat. No. 4,339,915 to Dammann et al discloses a false twist texturing apparatus comprising a pair of rotating discs which are biased toward each other by means of a movable piston. German Patent DE 33 06 594 discloses a similar yarn false texturing apparatus wherein the twisting movement imparted to the yarn by the piston of the friction false unit is adjusted as function of the yarn tension. In such a process, there are several reasons why the yarn tension may be too high or too low, and one of these reasons is the fact that the frictional forces imparted to the yarn by the friction false twist unit may be too high or too low. To overcome this deficiency, the cited German patent discloses a method wherein the yarn tension is measured, and the measured signal is fed to a control device. The control device in turn controls the pressure exerted by the piston, and the pressure exerted by the piston is adjusted such that fluctuations of the yarn tension are minimized. A similar process is shown in U.S. Pat. No. 4,145,871 to Iwata et al in which the frictional forces are adjusted by adjusting the distance of the two discs between which the yarn is twisted.
The above prior processes have the advantage of providing a relatively uniform yarn tension, but they also have a disadvantage in that a uniform yarn tension overlies and hides many other deficiencies which may disturb the uniformity of the texturing process. Such other deficiencies occur, for example, as a result of the wear of a feed system or a malfunction of the temperature control of the texturing zone. U.S. Pat. No. 4,720,702 to Martens discloses the broad concept of utilizing the yarn tension and the mean value of the yarn tension as part of a process for monitoring deficiencies in a yarn false twist texturing operation. In this concept, the yarn tension is continuously monitored and the mean value of the monitored yarn tension is continuously determined together with the differential between the monitored value and the mean value, and an alarm signal is generated whenever the mean value leaves a predetermined tolerance range or whenever the differential value leaves a second predetermined tolerance range. One of the alarm signals as described above monitors one or more of the deficiencies disturbing the uniformity of the texturing process.
However, the method as per U.S. Pat. 4,720,702 for detecting deficiencies cannot be applied, if the above-mentioned methods as per German Patent 33 06 594 or U.S. Pat. No. 4,145,871 are applied, because in these methods, the frictional forces applied to the yarn are adjusted in such a way that, irrespective of the kind of deficiency, all fluctuations of the yarn tensions are eliminated. This means that the yarn tension has a more or less constant mean value and the possibility of using the mean value or its fluctuation for determining certain deficiencies no longer exists.
It is accordingly an object of the present invention to provide a yarn false twisting process and apparatus wherein the impartation of twist may be controlled by measuring the yarn tension, and which also permits the quality to be monitored by measuring the yarn tension.